| This dissertation shows that pigmentary magnesium-rich coating systems can be devised to provide sacrificial cathodic protection to Al 2024 T-3/aerospace alloys in a mode analogous to that of zinc-rich systems for steel. Generally, conventional coatings formulated with traditional polymeric materials and "hazardous air pollutant" (HAP) solvents performed poorly in these Mg-rich systems in contrast with the novel silane-modified hybrid epoxy-urea polymeric materials containing non-HAP solvents. Moreover, through exploring siloxane chemistry, similar to those sol-gel systems, a hybrid epoxy-urea polymeric material was custom tailored and applied in a multi-layer fashion to an Al 2024 T-3 substrate for corrosion control that yielded performance properties surpassing those delivered by conventional technology.; Thus a new paradigm for corrosion protection of Al by Mg-rich pigmentation was obtained in a metal-rich coating system that provides proper film properties for use as an aerospace coating system. This Mg-rich coating system allows the replacement of traditional anti-corrosive systems that consist of three or four coats by a two-coat system, i.e., Mg-rich primer plus topcoat. The Mg-rich primer system consists of an initial amino-silane surface treatment applied to the alloy followed by application of polymeric materials, both organic and inorganic, in a binder matrix loaded with pigmentary Mg powder, formulated at or near the coating's critical pigment volume concentration (CPVC). The coating system is spray applied and cured at room temperature with minimum surface preparation requirements that underscores yet another convenient feature that it delivers. The final implication of this dissertation lies in this novel coating system's performance, its further refinement potential, and the overall convenience it delivers. Most importantly, in the interest of environmental acceptance, effectiveness, corrosion control, and ease of application, this system has demonstrated great potential as a corrosion coating for aluminum alloy 2024 T-3. |
